A wireless communication system typically provides one or more forms of wireless access to mobile access devices, enabling them to engage in voice and data communications with other devices—both wired and wireless—operating in or connected to the system, and to partake in various other communication services provided or supported by the system. The communication path from a mobile access device, such as a cellular telephone, personal digital assistant (PDA), or an appropriately equipped portable computer, for instance, to one or more other communication endpoints generally traverses a radio frequency (RF) air interface to a base transceiver station (BTS) or other form of access point, and on into a core transport network via a base station controller (BSC) connected to a mobile switching center (MSC) or to a packet data serving node (PDSN). The MSC supports primarily circuit voice communications, providing interconnectivity with other MSCs and PSTN switches, for example. The PDSN supports packet data communications, providing interconnectivity with packet-data networks, such as the Internet, via other packet-data switches and routers.
In a cellular wireless system, the BTS, BSC, MSC, and PDSN, among possibly other components, comprise the wireless access infrastructure, also sometimes referred to as the radio access network (RAN). A RAN is usually arranged according to a hierarchical architecture, with a distribution of multiple BTSs that provide areas of coverage (e.g., cells) within a geographic region, under the control of a smaller number of BSCs, which in turn are controlled by one or a few regional (e.g., metropolitan area) MSCs. As a mobile device moves about within the wireless system, it may hand off from one cell (or other form of coverage area) to another. Handoff is usually triggered by the RAN as it monitors the operating conditions of the mobile device by way of one or more signal power levels reported by the device to the RAN.
As the demand for wireless services has grown, and the variety of physical environments in which wireless access is provided becomes more diverse, the need for new topologies and technologies for coverage has become increasingly important. At the same time, alternative methods of wireless access, including WiFi and WiMax, are becoming more ubiquitous, particularly in metropolitan areas. Consequently, traditional cellular service providers are looking for ways to integrate different types of wireless access infrastructures within their core transport and services networks. In addition, as wireless access infrastructures of different service providers tend to overlap more and more within smaller spaces, the ability to share common infrastructure offers cost and operational benefits to network owners and operators.